One of the attack modes currently in military use is to discharge a projectile with a very flat trajectory, directed in azimuth to pass over a target, and then firing the projectile warhead when it is over the target. Top attack on targets such as tanks is desirable, since the top armor is usually thinner, the presented area is larger, the profile is flatter, and the engine of the vehicle is more vulnerable. The problem is to determine when the projectile has reached a point directly over the target.